Arc extinguishing means



July 27, 1943. G. F. McMAHoN 2,325,415

lARC EXTINGUISHING MEANS Filed Dec. 9, 1940 2 sheets-sheet 1 Inventar' July 27, 1943. s. F. MQMAHON ARC EXTINGUISHING MEANS Filed Deo. 9, 1940 2 Sheets-Sheet 2 6 P. J J w a n www@ ll l IQM f N mi s 5m wnfm Mm." wwf mi MMM 0mm www 54am f wn E G A N MMFL maw J n mL 4 r mM f A N l i i l l i n l \l l t i a l l l i l l l I Illllllll BINDER 0F METHYL CfLLl/LOSE G N .Mm mm L xr A MM A Patented July-27, 1943 Anc ExTiNGUIsinNG MEANS George F. McMahon, Chicago, lll., assignor to Schweitzer-t Conrad, Inc., Chicago, Ill., a corporation of Delaware Application December 9, 1940, Serial No. 369,162

My invention relates, generally, to circuit interrupting apparatus and ithas particular relation to arc extinguishing material used therefor and methods of making and moulding the same.

In electrical apparatus, particularly circuit interrupting devices, arc confining structures are provided around the path of the arc that is' formed on operation thereof. The surface of these structures which is subjected to the direct heat ofthe arc is preferably formed of a material which will evolve an arc extinguishing medium that will sweep out the arc, deionize the arc space and prevent its restrliking.

The material from which the arc extinguishing medium is' evolved should be of high dielectric strength both before and after operation of the circuit interrupter. In some instances a materia! may be satisfactory from an insulating standpoint before it has been subjected to the heat of an arc but afterwards it may be unsatisfactory because of the formation of a conducting path over its surface as a result of carbonization of some of the material. f'I'his is known as ftracking and is undesirable since aleakage path is provided over the surface of 'the arc confining structure which may result in a dangerous condition in the circuit in which the circuit interrupting device is connected.

For many applications in electrical circuit interrupting devices, such as expulsion fuse tubes, sleeves for replaceable fuse links and plugs of insulating material used for arc confining vpurposes, it is simpler and moregeconomical to extrude the arc extinguishing material into the desired shape. In so far as I am aware it has not been practicable in the past to extrudesome of the more desirable arc extinguishingV materials such as boric acid and magnesium berate.4

Circuit interrupting devices in which arc ex tinguishing materials are employed are used out of doors in many instances Where they are subjected to the weather. arc extinguishing material which is used be impervious `to water so that it will notswell, for example, and impair or prevent proper operation of the device.

An object of this invention is to reduce the carbon content of the insulating structure surrounding an arc path in a new and improved manner.

Another object of this invention is to provide for extruding arc extinguishing material into the desired shapes.

A further object of this invention is to provide water resistant arc extinguishing materials.

It is preferable that any 25 Claims, (Cl. 20o-120) Other objects of this invention will, in part, be obvious and in part appear hereinafter.

For a more complete understanding o f the nature and scope of this invention reference may be had to` the following detailed description taken in connection with the accompanying drawings in which:

Figure 1 is a longitudinal sectional view of a circuit interrupting device having separable contact members in which the present invention is incorporated;

Figure 2 is a`longitudinal sectional view of an l expulsion fuse device in which the present invention is incorporated;

Figure 3 is a view, in side elevation, of a replace-4 able fuse link, the insulating sleeve therefor beingshown in longitudinal section; l

Figure 4 is a view, partly in side elevation and partly in section, of a circuit interrupting device employing separable contact members and a plug of insulating material formed in accordance with the present invention for conflningand extin- Methyl cellulose is a Water` soluble celluloseether 'that is obtained by methylating cellulose such as cotton. Solutions of methyl cellulose are not affected by changes in acidity or alkalinity over a relatively wide range.

The arc extinguishing materials with which the binder of cellulose ether is employed are preferably those which will evolve water vapor and other gases when subjected to the heat of an arc. Certain inorganic materials are suitable for this purpose. Magnesium compounds such as magnesium borate, magnesium hydroxide, magnesium oxide and basic magnesium carbonate can be employed. Also, inorganic acids, such as boric acid, silicio acid, molybdic acid, and

arsenious acid, can be employed. Various combinations of these arc extinguishing materials can also be employed with the binder-of cellulose ether.

sieve.

vquite rigid and of such character that, when ex- Varying vamounts of the binding material are used depending upon the amount thatis necessary. The data thus far obtained indicates that it is unnecessary to employ more than by weight of methyl celluloseas the binder when the foregoing inorganic arc extinguishing materlals are employed. Usually, the amount of binder varies from 0.5% to about 4% by weight. Since a relatively small amount of binder is employed, it will be 'obvious that the carbon content thereof is negligible. Arc confining structures which are formed of one or-more of the foregoing inorganic arc' extinguishing materials with a binder of methyl cellulose are substantially free from trackingso that their dielectric properties are substantially unimpaired even after being subjected to repeated severe arcing.

In preparing the mix methyl cellulose is dissolved in water so as to produce a thick viscous liquid. 'I'he inorganic arc extinguishing material is added to the aqueous solution of methyl cellulose in powder form... Preferably the powder is ne enough to pass through a 200 mesh sieve, although satisfactory results can be obtained if it is capable of passing through only a 100 mesh 25 'Ihe resulting mixture is very thick and truded or formed to the desired shape, it is capable of retaining the same after the extruding apparatus has been removed so as to permit removal of the extruded shape for drying and aging.

Methyl cellulose is supplied commercially in four different viscosity grades in the form of white fibers, namely, low, mediumj high,

and extra high viscosity types. The lowv grade requires more per unit volume of water to make a thick viscous solution than the "extra high grade to make a solution of the same viscosity. In other words, when a solution of high methyl cellulose or solid content is desired, the low grade is used and when a low solid content is desired the extra high grade is used. This is important since the strength, shrinkage, etc., are partly controlled by adjusting this factor to suit the needs.

Standard methyl cellulose stock solutions can be made up as indicated in the following table, dissolving the material in cold water or by adding hot water at the start and then cold water.

The dried, finely divided powder is placed in a mixer and the correct volume of any selected methyl cellulose solution added and the whole thoroughly kneaded and mixed. If more than one powder is used, the powders are mixed in the dry state before adding the methyl cellulose time still be able to form the object desired. This is to reduce shrinkage on drying out.

Methyl cellulose mixtures have the property of making an easy owing plastic body when subjected to pressure without the water being squeezed out of the compound or plugging up the mold cavity or extrusion nozzle through separation of the solids from the water.

'Ihe following are' examples of various mixes that can be made according to the present invention which are suitable for extruding purpos'es.

Example No. 1

70 grams of 100 mesh or ner magnesium hydroxide powder were added `to 52 grams of a 5% methyl cellulose solution, using the low viscosity grade. The whole was kneaded and mixed thoroughly and placed in an extruding or pressure tool and formed into rods or cylinders of approximately 5/3" O. D. which were then baked at 6080'C. and dried. The resulting product contained about 3.5% methyl cellulose and the balance was magnesium hydroxide.

Example No. 2

'at 60-80" C. with or without a vacuum for several hours. The product was a good arc extinguishing material and a good insulator when tested at high voltages. This product when dry contains approximately 1.59% methyl cellulose and the balance magnesium borate.

Example No. 3

45I grams of 100 mesh or ner magnesium borate powder were mixed with 5 grams heavy magnesium oxide mesh or finer powder. To this was added 26 grams of a very thick solution of low viscosity methyl cellulose containing 8% of methyl cellulose. The whole was kneaded and mixed thoroughly and used to line larger diameter tubes than those of Example 2 above, the liner in this case being 5/8" I. D. x O. D. x 4% long.

The dried tube liner after baking at (iO-'70 C. contained-approximately 3.7% methy1 cellulose and the balance magnesium borate and magnesium hydrate in the following proportions: magnesium borate 83.0% and magnesium hydrate 13.3%. During this process, the major portion of the magnesium oxideis converted into the hydrate because of the reaction with the water of the methy1 cellulose solution.

Example No. 4

25 grams of magnesium oxide and 75 grams of magnesium borate powders were thoroughly mixed and to this was added 44 grams of a 5% aqueous solution of low viscosity grade methy1 cellulose. The whole was thoroughly kneaded and mixed and inserted in an extrusion press and used to form tube liners 1% I. D. x` O D. x 8%" long and also rods .617" O. D. x 2% long. On drying the tube liners shrank 312'.' in length and therod diameter decreased .012. No cracks appeared in either the tubes or rods.

The vfinal composition, calculating to a dry basis was as fol1ows: magnesium borate 66.14%, magnesium hydrate 36.18%, and methyl cellulose 1.94%. As in Example No. 3, the greater portion of the magnesium oxide is converted into th hydrate.

Example No.

111 grams of pure boric acid powder which passed through a 100 mesh sieve were mixed with 55 grams of a 2.5% extra high grade methyl cellulose aqueous solution. The whole was thoroughly kneaded and mixed and used to form small rods, about M1," 0. D. and tubing O. D. with ai," wall inside other insulating tubing. The methyl cellulose content on a dry basis was approximately 1.22% by Weight.

Liners using methyl cellulose binder can be extruded in glass and porcelain tubes as well as into tubes formed of organic insulating material such as i'lber or phenolic condensation material.

Liners for insulating tubes are extruded by placing a core of suitable material such as metal inside of the housing in which the liner is to be extruded and centering the same therein. The housing with the core therein is suitably held in extruding apparatus and the material for forming the liner is forced into the space between the core and the inner surface of the housing. After the space has been iilled, the core is withdrawn and the housing is placed in an oven where it is baked to drive off excess moisture.

Liners that are formed of magnesiumborate with a binder oi methyl cellulose are substantially free from cracks and have good mechanical. and arc extinguishing properties. Because the amount-of methyl cellulose binder comprises a relatively small part of the liner, the amount of carbon that is deposited is negligible and consequently it is substantially free from tracking.

Rods or plugs can be satisfactorily formed of magnesium hydroxide with a binder of methyl are highly resistant to water Tubes or'liners can be formed using varying amounts of magnesium borate and magnesium oxide with a binder of methyl cellulose. In this combination of materials magnesium hydrate is formed through the reaction between the oxide and the water used to carry the methyl cellulose. This reduces the setting time of the plastic mass. The resulting structure is somewhat stronger than if magnesium borate alone were used and it is less likely to crack than is the case if magnesium oxide alone were used.

Referring now particularly to Figure l of the drawings, it will be observed that the reference character I0 designates, generally, a housing or sleeve of insulating material for a circuit interrupter. The housing I0 is formed by an outer layer il of suitable insulating material such as a synthetic plastic or ceramic material, i. e., glass or porcelain, while the inner layer or liner I2 is formed of arc extinguishing material comvbined with a binder as described hereinbefore. kThe liner i2 may be extruded into the outer sleeve or housing il, as previously described, after which it is suitably dried' and aged.

At one end of the housing ill is a stationary contact member or terminal i3 which is arranged to be engaged by a movable contact'member or terminal I4. It will be understood that the contact members I3 and I4 are connected in an electric circuit whichis to be interrupted and that, when the circuit is interrupted under load conditions, an arc will be formed between the contact members I3 and i4. The heat of the arc will cause an arc extinguishing medium, i. e., water vapor, to be evolved from the inner surface of the liner I2 which acts to deionize the arc space between the contact members I3 and I4 so as to prevent the arc being restruck.

Referring now particularly to Figure 2 oi' the drawings, it will be noted that the reference character I5 designates, generally, an expulsion fuse tube which has an outer layer I8 of insulating material, such as a synthetic plastic body or a ceramic material, and an inner layer I1 that is formed of arc extinguishing material in the manner previously described. The outer layer I6 is provided with a plurality of peripheral grooves I8 in its inner surface into which the plastic mass forming the inner layer I1 is extruded for holding the same in place.

At the upper end of the fuse tube I5 is a terminal I9 which is apertured so as to receive a fuse link, indicated generally at 20, therethrough. The fuse link 20 is universal in'character and includes arelatively infusible terminal 2| having a threaded stud portion 22 for receiving a ilanged head 23 that rests against the upper end of the terminal I9. A cap 24 is arranged, as shown, to be screwed on to the terminal I9 for holding the flanged head 23 in place. A strain element 25, formed of relatively high strength wire, such as nickel chromium alloy wire, and a fusible element 26, formed preferably of silver, are secured to the lower end of the relatively infusible terminal 2|. The other ends of the strain and fusible elements 25 and 26 are secured in the upper end of another relatively infusible terminal 21 to which isseoured a exible conductor 28. The flexible conductor 28 extends out of the lower end of the expulsion fuse tube 26 and is connected to a second terminal 29 thereon by suitable clamp means 30.

When the liner I1 is formed of arc extinguishing material as disclosed herein, tests have shown that it is unnecessary to provide an additional sleeve of insulation for closely surrounding the strain and fusible elements 25 and 26 as is now generally considered necessary in the construction of universal fuse links. Even on relatively low current arcs, because of the relatively great availability of the water vapor in the liner I1, a suflicient amount of the arc extinguishing vmedium is evolved to. sweep out the arc and deionize the arc space.

In Figure 3 of the drawings, there is shown generally at 33 a' universal type linkin which the present invention is incorporated. lThe fuse link 33 comprises a. relatively infusible terminal 34 which is provided with a threaded stud portion 35 for receiving a flanged head 36. A strain element 3l and a fusible element 38, of material similar to' the strain and fusible elements 25 and 2S, respectively, of Figure 2, are connected to the lower end of the terminal 34 and to the upper end of another relatively infusible terminal 39. A iiexible conductor do is secured to the lowerL end of the terminal 39 and it is provided with a specialcone tting di for adapting the fuse link 33 for use with certain types of fuse y devices that are now well known to those skilled In Figure 4 ofthe drawings there is shown a circuit interrrupting device which forms a part of a load break switch structure, the details of which are fully disclosed in the copendlng application of Lindell et al., Serial No. 349,898,

filed August 2, 1940. The load break device 4BA is intended for use with a disconnecting switchy and is employed for eecting the ilnal circuit interruption. However,l its uses 'are not limited to this particular application. y

The switch 48 comprises a vstationary contact member 49 that is generally ring-like in character and itis arranged to be engaged by a rodlike contactmember 50 that is disposed to be moved through a bore El Athat is provided by an extruded plastic liner 52 which .is formed as described hereinbefore using methyl cellulose as a binder for the arc extinguishing material. The

liner 52 is held in place by a housing 53 of suitable insulating material such as a synthetic plas-` tic or a ceramis material in which grooves 54 may beprovided for the purpose indicated hereinbefore. The rod-like contact member 58 is arranged to be moved out of and into contact engagement with the contact member 49 by means of, an operating memberli, only a portion of ,which is shown. Any suitable operating means assaeie scription or shown in the accompanying drawings shall be -interpreted as illustrative and not in a limiting sense.-

What is claimed as new is:

1. In electrical apparatus, a conductor from which an arc may be drawn, and arc extinguishing material along the path of the arc from which .an arc extinguishing medium is evolved due to the heat of the arc for extinguishing the same, said arc extinguishing material including a binder of a water soluble cellulose ether.

2. In electrical apparatus, a conductor from which an arc may be drawn, and arc extinguishing material along the path ofthe arc from which an arc extinguishing medium is evolved due to -the heat of theA arc for extinguishing the same,

said arc extinguishing Imaterial including a binder of methyl cellulose.

3. In electrical apparatus, a conductor from which an arc may be drawn, and'inorganic arc extinguishing material along the path of the arc L from which an arc extinguishing medium is evolved due to the heat of the arc for extinguishing the same,said arc extinguishing material in-l cluding a binder of a water soluble cellulose ether.

4. In` electrical apparatus, a conductor from which an arc may be drawn, and inorganic arc extinguishing material along thepath of the arc from which anv arc extinguishing medium is evolved due to the heat of the arc for extinguishing the same, said arc extinguishing may terial including a binder of methyl cellulose.

5. In electrical .apparatuaa conductor from which an arc may be drawnL/arc extinguishing materialalong thevpath of th arc from which an can be provided for moving the rod-like contact .member 50.

It will be understood that, when the rod-like contact member is moved away from the stationary contact member 49 under load, an arc will be formed within the bore 5l which should arc extinguishing medium is'evolved due to vthe the heat of the arc for extinguishing the same and comprisinga magnesium compound and a" binder therefor of a water soluble cellulose ether;

6. In electrical apparatus, a conductor from which an arc may be drawn, arc extinguishing material along the path of the arc from which anv arc extinguishing medium is evolved due to be promptlyexnguished S0 aS 170 quikly effect 45 'the heat of the arc for extinguishing the same, said arc extinguishing material being selected circuit interruption with a minimum of disturbance. In order to effect this result an insert 58 is carried by and is movable with the rod-like ycontact member Eiland it is moulded into a plug 51 of arc extinguishing ma'terial having a binder of methyl cellulose that is formed as previously described. That is, the plug 57 is extruded around the insert 56. The plug 5l moves together with the rod-like contact member 50 and substantially fills the bore 5| so that the arc which is drawn between the contact members 49 and 50 is confined between the outer surface of the plug 56 and the inner surface of the liner 52. Under these circumstances the arc is quickly blown out and the arc spacelis deionized so as to prevent restriking.

In Figure 5 of the drawings there is shown a plug 58 which can be used, if desired in lieu of theV plug 5l. It will be observed that the'plug 58, instead of having an insert extruded vor moulded into thesame, is drilled and tapped as in-combination, means between which an arc is g indicated at 59 for receiving a threaded stud.

The plug 58 is formed of arc extinguishing material with4 a binder o f methylncellulose in a manner previously described; v v

Since certain further changes can be made in the aboveconstructions and diil'erent embodil ments of the invention can be made without departing from the scope thereof, it is intended that all matter contained in the foregoing defrom the group consisting of magnesium borate, magnesium hydroxide, magnesium oxide, basic magnesium carbonate and boric acid, and a binder for said arc extinguishing material comprising from a small 'but effective amount up to 5% of its weight of a water soluble cellulose ether.

7. An electric circuit interrupter comprising, in combination, mean.; between which an arc is formed on interruption of the circuit, arc ext material adapted to conilne the arc and to evolve an arc extinguishing medium due to the heat thereof, and a binder of methyl cellulose for. said arc extinguishing material.

8. An electric circuit interrupter comprising,

formedon interruption of the circuit, arc extinguishing material comprising a magnesium heat thereof, and a binder of water` soluble cellulose ether for said arc extinguishing material.

9. An' electric circuit interrupter comprising,l

in combination, means between whichan arc is formed on interruption of the circuit, arc extinguishing material. adapted to confine the arc and to evolve an arc extinguishing medium due to the heat thereof, said arc extinguishing material being selected from the group consisting of magnesium borate, magnesium hydroxide.'

magnesium oxide, basic magnesium carbonate and boric acid, and a binder for said arc extinguishing material comprising from a small but effective amount up to of its Weight of water soluble cellulose ether.

10. 'An electric circuit interrupter comprising, in combination, means between which an arc is formed on interruption of the circuit, and a structure adapted to conne said arc including magnesium borate, magnesium hydroxide and a binder therefor of methyl cellulose.

l1. An electric circuit interrupter comprising, in combination, means between which an arc is formed on interruption of the circuit, and a structure adapted to conne said arc including magnesium borate, magnesium oxide and a binder therefor of methyl cellulose.

12. An electric circuit interrupt-er comprising, in combination, means between which an arc is formed. on interruption of the circuit, and a structure adapted to confine said arc including magnesium borate, boric acid and a binder therefor of methyl cellulose.

13. An electric circuit interrupter comprising, in combination, means between which an arc is formed on interruption of the circut, and a structure adapted to conne said arc including an insulating inorganic acid and an organic binder.

14. A housing for confining an arc comprising a tube formed of ceramic insulating material having a liner formed of from a small but eiective amount up to 5% of methyl vcellulose and the balance selected from the group consisting of magnesium borate, magnesium hydroxide, magnesium oxide and boric acid.

15. A lfuse device comprising, in combination, means adapted to fuse and form an arc on the occurrence of an overload in an electric circuit, a structure surrounding and confining the arc including arc extinguishing material adapted to evolve an arc extinguishing medium due to the heat of the arc, and a binder of a water soluble cellulose ether for said arc extinguishing material.

16. A fuse tube having its inner surface formed by a material selected from the group consisting of magnesium borate, magnesium hydroxide,

magnesium oxide, basic magnesium carbonate and boric acid, and a binder therefor of methyl cellulose.

17. A replaceable fuse link comprising, in combination, a. pair of spaced.terminal members, fusible means interconnecting said terminal members, and an insulating sleeve surrounding said fusible means having its inner surface formed by a material' selected from the group consisting of magnesium borate, magnesium hydroxide, magnesium oxide, basic magnesium carbonate and boric acid and a binder therefor of methyl cellulose. Y

18. An electric circuit 'breaker comprising, in

combination, separable contact members between which an arc may be drawn on separation thereof, a sleeveI of insulation into which the arc is drawn, and a plug disposed to be moved into said sleeve for confining said arc between its outer combination, separable Contactl members between which an arc may be drawn on separation thereof, as'leerve 'oi insulationldnto which the arc` is drawn, and a plugtdis'posedto be moved into said sleeve for confining sai'ifarc between its outer surface and the inner(sur-.taceb of said sleeve, said plug having its outer surface and said sleeve having its inner surface formed by material selected from the group consisting of magnesium borate, magnesium hydroxide, magnesium oxide, basic magnesium carbonate and boric acid,and a binder therefor co-mprisingyrom a small but effective amount up to 5% of its weight tof methyl cellulose.

20. An arc extinguishing material comprising from a small but effective amount up to 5% oi water soluble cellulose ether and the balance seA lected from the group consisting of magnesium borate, magnesium hydroxide, magnesium oxide, basic magnesium carbonate and boric acid.

21. An arc extinguishing materal comprising from a small but effective amount'up to 5% of methyl cellulose and the balance selected from the group consisting of magnesium borate, magnesium hydroxide, magnesium oxide, basic magnesium carbonate and boric acid.

22. An arc extinguishing material comprising a water insoluble inorganic material and a water soluble cellulose ether.

23. An electric circuit interrupter comprising, in,combination, means between which an arc is formed on interruption ofthe circuit, and a structure adapted to conne said arc including an inorganic solid arc extinguishing material and a in combination, means between which an arc is formed on interruption of the circuit, and a structure adapted to confine said arc including boric acid and a water soluble organic compound.

GEORGE F. McMAI-ION. 

